1. Field of the Invention
The invention relates to a method of monitoring a flow behaviour of components to be mixed, a control system and methods for detecting settled solids at a mixing impeller.
2. Related Art
Biopharmaceutical manufacturing requires mixing at several process steps, for example media preparation, buffer preparation, low pH viral inactivation of material between process steps. For this mixing step, usually the components to be mixed are accommodated in a mixing vessel in which a mixing impeller is provided. The mixing impeller is driven by a motor so that the mixing impeller is rotated. The mixing impeller usually comprises a rotationally symmetric mixing impeller basis and at least one mixing impeller blade that is attached to the mixing impeller basis. The mixing impeller blade extends radially or axially with respect to a rotation axis from the mixing impeller basis. The geometry and size of the mixing blade are chosen depending on the mixing application. For example, the mixing blade may be straight, curved and/or backswept with respect to the rotation axis of the mixing impeller.
The mixing vessel may be a rigid or flexible container. A rigid mixing vessel is used mostly as a reusable container, while flexible mixing vessels are used mostly as a single-use container.
The mixing impeller inside of the mixing vessel may be connected to the motor via a driving shaft that extends through the mixing vessel side wall. However, some applications require that the mixing equipment is fully closed with no possibility of leakage between the mixing vessel and the environment—for example, the fluids to be mixed are either hazardous (e.g. toxic) or if they are sensitive to contamination from the outside environment (e.g. highly purified pharmaceutical material). In such cases, a magnet drive system may be employed as a means of transmitting torque between an external motor and a mixing impeller inside of the mixing vessel. A driving magnet at the outside of the mixing vessel is driven by the external motor, and a follower magnet is arranged inside of the mixing impeller in the mixing vessel.
In contrast to the conventional mixing equipment, in which mixing vessels typically are fabricated from stainless steel or other alloys, single-use systems comprise plastic bags as mixing vessels and are used only once. Single-use systems are used increasingly in biopharmaceutical manufacturing operations because of the increased flexibility, lower capital cost, elimination of cleaning steps, reduced risk of cross-contamination, and reduced utility burden.
When mixing two or more components in a mixing vessel (e.g. liquid-liquid, liquid-solid), there may be a desired viscosity or density of the components to be mixed. Alternatively, there could be a viscosity or density range that is to be avoided.
Therefore, a method is required that allows the determination of the density and viscosity of the components to be mixed without requiring additional instrumentation or sampling so that the density and viscosity of the components to be mixed are monitored.